JavaScript自定义排序功能，用于确定字母的优先级

Question

I already have a sorted array (can contain up to 1,000 items), I just want to take the block of items that start with the specified character and move them to the top.

// Before sort
{ "alpha", "beta", "delta", "delta frequency", "gamma", "theta" } 

// After sort with "d" as the specified letter
{ "delta", "delta frequency", "alpha", "beta", "gamma", "theta" }

I'm not familiar enough with JavaScript to know a good way to do this. My first thought was to iterate through each item and see if the index of the specified start character was "0" to find the first and last array index, and moving that range to the top of the array, but that seemed like it might be wasteful. Is there a better way?

Answer 1

var array = [ "alpha", "beta", "delta", "delta frequency", "gamma", "theta" ];
var startingWithD = array.filter(function(s) {
    return s[0] == "d";
});
var others = array.filter(function(s) {
    return s[0] != "d";
});
array = startingWithD.concat(others);

Answer 2

Here's an option:

function sortWithPriority(arr, letter) {
    var numFound = 0,
        i = arr.length,
        cur;
    while (i-- > numFound) {
        cur = arr[i];
        if (cur.charAt(0).toLowerCase() === letter.toLowerCase()) {
            arr.unshift(arr.splice(i, 1)[0]);
            numFound++;
            i++;
        }
    }
}

DEMO: http://jsfiddle.net/kU8wK/

It will remove any item that starts with the letter specified, and moves it to the beginning of the array. So the array is modified in place.

It could easily be modified to allow the passing of a string (not just a letter) that the item must start with.

UPDATE:

As for performance, when it comes to the current answers of this question, this method seems fastest.

Here's the performance test I made: http://jsperf.com/sort-with-letter-priority

It uses an array with hundreds of items in alphabetical order (better test case than 10 or so). It may not be the best way to generate the array, but it does it correctly and that part is unrelated to the actual timing anyways (it runs outside of the timing).

Note that my function is modified to not use toLowerCase , so that all functions should be "equal" when comparing the first letter to the targeted letter. Of course, if you want it to be more accurate, in the case that the first letter of the items in the array could be upper case (or you pass an upper case letter), you'd have to use toLowerCase on both to get an accurate comparison. For the performance test, I left out that possibility for all test cases.

Answer 3

Here's a sorting algorithm, which will actually sort the array weighting strings that start with "d" to the beginning. Note that I've rearranged the beginning array a bit, to show that the sorting works correctly.

array = [ "beta", "alpha", "delta frequency", "delta 2", "delta 1", "delta", "gamma", "theta" ];
array.sort(function(a,b) {
    if (a[0] == "d" && b[0] != "d") {
        return -1
    }
    if (b[0] == "d" && a[0] != "d") {
        return 1;
    }
    return a > b;
});

console.log(array);

http://jsfiddle.net/ryanbrill/RqfgL/